The experiments described in this proposal are directed at identifying the cellular transport processes involved in intracellular pH (pHi) regulation in the principal and intercalated cells of the rabbit cortical and outer medullary collecting tubule and the S1, S2 and S3 segments of the proximal tubule of the rabbit kidney. I will use the isolated perfused tubule preparation, a recently developed videomicrofluorometer and the pH probes 1,4 DHPN or BCECF to measure pHi in individual cells. First, the transport processes involved in pHi regulation will be determined. Second, the coupling of energy metabolism to work output, and the substrate specificity of this process will be assessed by measuring the fluorescence of NADH in individual cells. The results will increase the understanding of bicarbonate transport in the proximal tubule and the collecting tubule which will be important in understanding various pathophysiologic states of acid-base homeostasis which affect the nephron.